Spring loaded module for cooling integrated circuit packages directly with a liquid

ABSTRACT

A liquid cooled circuit module comprises an integrated circuit package; a cover having a rim which lies against the integrated circuit package, the cover being shaped to form a passage for the liquid between the integrated circuit package and the cover; a retaining mechanism, which is fastened directly to the integrated circuit package, and which includes a member that extends above the cover; and a spring, which is held in compression between the cover and the retaining mechanism member; the spring being adapted to press the rim against the integrated circuit package with at least a predetermined minimal force which prevents leaks and at the same time not exceed a stress limit in the spring. In one embodiment of the module, the retaining mechanism includes headed pins which are fixedly attached to the integrated circuit package; the retaining mechanism member has tapered openings which are aligned with the pins and in which the headed pins removably lock; and the spring is adapted to maintain at least the predetermined minimal force on the rim and simultaneously not exceed the stress limit even under the condition where the spring is compressed by a variable distance due to several manufacturing tolerances within the module.

BACKGROUND OF THE INVENTION

This invention relates to systems for cooling electrical components; andmore particularly, it relates to systems for cooling integrated circuitpackages with a liquid in a digital computer.

Initially in the prior art, integrated circuits in digital computerswere cooled by convection with air. Typically, the integrated circuitsof the computer were mounted on several printed circuit boards which inturn were mounted in a frame. Then one or more fans were provided withinthe frame to simply blow air across the integrated circuits. Such acooling system is relatively inexpensive; however, it also has severalmajor limitations.

For example, as the amount of circuitry on an integrated circuit chipincreases, the amount of power and the amount of heat which that chipdissipates also increases. Thus a point is eventually reached with verylarge scale integrated circuits or with multichip integrated circuitpackages at which the power dissipation is simply too high to allowcooling by air convection. Also, the logic gates in integrated circuitpackages operate at slower speeds as their operating temperature israised. Further, integrated circuits are more prone to failure when theyare operated at higher temperature.

Accordingly, in the prior art, systems for cooling integrated circuitsby conduction with a liquid have been developed. One such system whichIBM uses for example in their 3081 computers, consists essentially of aplurality of 3081 multichip cooling modules. Each module includes a baseplate, a substrate with several integrated circuit chips, a pistonholding plate, and a cold plate with water channels. These items arebolted together one on top of the other in the above recited order.

Formed in the piston holding plate are several cylinders, each of whichcontains a helical spring and a piston. In operation, each spring pushesa piston against a respective integrated circuit chip on the substrate;and heat from each chip then travels in a serial fashion through thepiston, through the cylinder sidewalls, and into the cold plate to thewater.

However, cooling in this IBM module is still substantially limitedbecause the water does not flow directly over the surface of theintegrated circuit chips, and because thermal conduction between apiston and a cylinder sidewall is poor. In addition, liquid can leakfrom the cold plate at its input port or its output port when adefective connection is there made since the liquid passes through thecold plate under high pressure.

In another liquid cooling system, which is used in Cray-2supercomputers, multichip circuit modules are completely immersed in aliquid bath. But this makes it cumbersome to remove a module for repair.Also, only inert liquids can be used; otherwise conductive traces whichinterconnect the circuit chips will corrode. Further, the liquid musthave a very low dielectric constant so that electrical signals on theconductive traces do not propagate slowly. To meet these requirements,Cray-2 uses a special liquid called FC-77. But its surface tension isfour times smaller than the surface tension of water; and this placesconsiderable demands on the seals and gaskets in the coolingsystem--otherwise they will leak.

Accordingly, a primary object of the invention is to provide an improvedliquid cooling module for integrated circuit packages in which all ofthe above problems, and others, are overcome.

BRIEF SUMMARY OF THE INVENTION

In accordance with the present invention, a liquid cooled circuit modulecomprises an integrated circuit package; a cover having a rim which liesagainst the integrated circuit package, the cover being shaped to form apassage for the liquid between the integrated circuit packages and thecover; a retaining mechanism, which is fastened directly to theintegrated circuit package, and which includes a member that extendsabove the cover; and a spring, which is held in compression between thecover and the retaining mechanism member; the spring being adapted topress the rim against the integrated circuit package with at least apredetermined minimal force which prevents leaks and at the same timenot exceed a stress limit in the spring.

In one embodiment of the module, the retaining mechanism includes headedpins which are fixedly attached to the integrated circuit package; theretaining mechanism member has tapered openings which are aligned withthe pins and in which the headed pins removably lock; and the spring isadapted to maintain at least the predetermined minimal force on the rimand simultaneously not exceed the stress limit even under the conditionwhere the spring is compressed by a variable distance due to severalmanufacturing tolerances within the module.

BRIEF DESCRIPTION OF THE DRAWINGS

Various features and advantages of the invention are described in detailin the Detailed Description in conjunction with the following drawingswherein:

FIG. 1 illustrates a leak tolerant liquid cooling system for electricalcomponents which is constructed in accordance with the invention;

FIGS. 2A-2D illustrate the operation of the FIG. 1 system under thecondition where an air leak develops in a conduit within the system;

FIGS. 3A-3D illustrate the operation of the FIG. 1 system while aprinted circuit board is removed from the system;

FIG. 4 is a set of equations which show how the FIG. 1 system operatesat subatmospheric pressures when a pump in the system is running;

FIG. 5 is a set of equations which show how the FIG. 1 system operatesat subatmospheric pressures when a pump in the system is off;

FIG. 6 is a sectional view of an embodiment of a cooling module withinthe FIG. 1 system;

FIG. 7 is a top view of the cooling module of FIG. 6;

FIG. 8 is a set of equations which describe how a spring within thecooling module of FIGS. 6 and 7 operates; and

FIG. 9 is a sectional view of another embodiment of a cooling modulewhich is suitable for use within the FIG. 1 cooling system.

DETAILED DESCRIPTION OF THE INVENTION

A preferred embodiment of the invention will now be described inconjunction with FIG. 1. That embodiment includes a frame 10 in which aplurality of printed circuit boards 11 are mounted. Only one of theboards 11 is shown in FIG. 1, but the remaining boards are disposed in aparallel fashion behind the illustrated board. These boards are held inplace by card guides 12 and they plug into a backplane 13.

Also included in the FIG. 1 embodiment is a top reservoir 14 which isattached to frame 10 above the printed circuit boards. This reservoir 14has an opening 14a which causes any liquid in the reservoir to be atatmospheric pressure. Lying below the printed circuit boards 11 is abottom reservoir 15. This reservoir 15 is airtight except that itincludes a valve 16 which can be opened to place the bottom reservoir atatmospheric pressure.

A conduit 17 is also included in the FIG. 1 embodiment. It runs from thetop reservoir 14, over the printed circuit boards 11, to the bottomreservoir 15. In operation, liquid from the top reservoir 14 passesthrough the conduit to the bottom reservoir; and in so passing theliquid cools the electrical components on the printed circuit boards.

Several parts 17a thru 17h make up the conduit 17 as indicated inFIG. 1. Items 17a and 17h are valved couplers; items 17b and 17g areflexible tubes; items 17c and 17f are metal or plastic manifolds; items17d are cooling modules for the electrical components; and items 17e aretubes for interconnecting the cooling modules. A separate conduit 17 isprovided for each of the printed circuit boards.

Liquid in the bottom reservoir 15 passes through a pipe 18 to a pump 19.This pump sucks the liquid from the top reservoir through the conduit 17to the bottom reservoir. Then the pump 19 returns the liquid back to thetop reservoir 14 through a pipe 20, a heat exchanger 21, and anotherpipe 22.

Two level sensors 23 and 24, along with a relay circuit 25, are alsoincluded in the FIG. 1 system as shown. They control the operation ofthe pump 19 as well as the valve 16. Sensor 23 detects when the level ofthe liquid in the bottom reservoir 15 is at a predetermined high level,whereas sensor 24 detects when that liquid is at a predetermined lowlevel.

Circuit 25 responds to the level sensors 23 and 24 by generating acontrol signal S₁ on conductors 26a which turn the pump 19 on, beginningwhen the liquid in the bottom reservoir 15 is at the high level, andcontinuing until the liquid in the bottom reservoir is at the low level.During this time, valve 16 is closed.

Conversely, circuit 25 generates a control signal S₂ on conductors 26bwhich open valve 16 beginning when the liquid in the bottom reservoir 15is at the low level, and continuing until the liquid in the bottomreservoir reaches the high level. During this time, pump 19 is off.

Reference should now be made to FIGS. 2A-2D which illustrate theoperation of the FIG. 1 cooling system under the conditions where asmall leak develops in the conduit 17 on one of the boards 11.Initially, as shown in FIG. 2A, there are no leaks, and liquidcirculates through the system in a normal fashion. In this state, theliquid is sucked by the pump 19 from the top reservoir 14 through therespective conduits 17 on the printed circuit boards 11 to the bottomreservoir 15; and simultaneously, the liquid is pumped back to the topreservoir.

Subsequently, as shown in FIG. 2B, a small leak develops in the conduiton one of the printed circuit boards 11i. This leak may be caused, forexample, by a faulty seal in a liquid cooling module 17d; or it could becaused by a faulty connection between a tube 17e and a cooling module.

When such a leak occurs, fluid does not squirt out of the conduit.Instead, air is sucked into the conduit 17 because, as will be explainedin conjunction with FIG. 4, the liquid flows through the conduit 17 atsubatmospheric pressures. Air which is sucked into conduit 17 passes tothe bottom reservoir 15 where it accumulates. Thus, as shown in FIG. 2B,the liquid level in the bottom reservoir 15 drops at a rate which isproportional to the rate at which air is leaked into the conduit.

If the leak is small in comparison to the size of the bottom reservoir15, several hours may pass before the liquid in the bottom reservoirgets to the predetermined low level. During this time, the liquidcontinues to flow through the conduit 17 and cool the electricalcomponents on the printed circuit boards. Eventually, however, the stateof FIG. 2C is reached in which sensor 24 detects that the liquid levelin the bottom reservoir 15 is too low.

In response, pump 19 is turned off and valve 16 is opened. Consequently,liquid is no longer pumped from the bottom reservoir 15. But liquid doescontinue to flow from the top reservoir, due to gravity, through theconduit 17 and into the bottom reservoir 15. Thus, as shown in FIG. 2D,the bottom reservoir 15 begins to fill up, and this purges the air fromthe bottom reservoir through valve 16.

When the liquid in the bottom reservoir 15 reaches the predeterminedhigh level, it is detected by sensor 23. In response, pump 19 turns onand valve 16 closes. This returns the operation of the system back tothat which is shown in FIG. 2A. Thus the system will continue to cyclethrough the operating modes of FIGS. 2A-2D until the air leak in conduit17 is fixed.

Turning next to FIGS. 3A-3D, they show a sequence by which board 11i maybe removed from the system without interrupting the cooling system'soperation. Initially, as shown in FIG. 3A, board 11i is disconnectedfrom the top reservoir 14. This is achieved via the valved coupler 17aas is shown in FIG. 1. Such a coupler should have a valve on the portwhich connects to the top reservoir 14 and no valve on the port whichconnects to the board 11i.

When board 11i is disconnected as shown in FIG. 3A, A large amount ofair will be sucked through the conduit 17 on board 11i into the lowerreservoir 15. At the same time, any liquid in the conduit on board 11iwill drain into the lower reservoir.

Thus, a state is quickly reached, as shown in FIG. 3B, in which sensor24 detects that the liquid level in the lower reservoir is too low. Thenpump 19 turns off and valve 16 opens. Consequently, as shown in FIG. 3C,the liquid from the top reservoir 14 starts to fill the bottom reservoir15 due to gravity, and this purges the air from the bottom reservoir.

During the time that the bottom reservoir is being filled, board 11iwith its empty conduit 17 can be disconnected from the bottom reservoir15. This is achieved via the valved coupler 17h as shown in FIG. 1. Sucha coupler should have a valve on the port which connects to the bottomreservoir and no valve on the port which connects to the board.

FIG. 3D shows the result of the above disconnecting step. Also, as shownin FIG. 3D, the system will continue to operate in its normal fashionwith board 11i removed after the sensor 23 detects that the bottomreservoir is full and turns pump 19 back on.

Consider now FIG. 4 which is a set of equations that shows how thepressure in the fluid of the FIG. 1 system varies as it travels from thetop reservoir 14 to the bottom reservoir 15. Equation 1 is Bernouilli'sequation as applied to the FIG. 1 system between two points "a" and "b".Point "a" is at the surface of the fluid in the top reservoir and point"b" is at an arbitrary one of the components 17d and 17e on circuitboard 11. In equation 1, P is fluid pressure, ρ is fluid density, V isfluid velocity, g is gravity, h is height, and L is pressure losses.

Equation 1 can be simplified if the top reservoir 14 is made largerelative to the flow rate of fluid from that reservoir. This reduces thevelocity of the fluid in the top reservoir to essentially zero as statedby equation 2. Substituting equation 2 into equation 1 and solving theresult for the pressure P_(b) yields equation 3.

In equation 3, the term P_(a) is atmospheric pressure since the topreservoir 14 is open to the atmosphere. Thus, in order for the pressureat point "b" to be subatmospheric, the sum of the two rightmost terms inequation 3 must be larger than the third term from the right. This isstated by equation 4.

All of the remaining equations 5 thru 15 give an example of how theconstraint of equation 4 can be met. Initially, one should pick the flowrate Q of the fluid through each of the cooling modules 17d such thatthe electrical components are properly cooled. For example, as stated inequation 5, one suitable Q is 25 milliliters per second.

From the quantity Q, the total flow rate Q_(T) through valve 17a can becalculated simply by multiplying Q by the number of parallel outputports from the manifold 17c. For example, if there are eight outputports, then the total flow rate Q_(T) through valve 17a is 200milliliters per second, as stated by equation 6. This flow rate Q_(T) isachieved by properly selecting the pump 19.

Given Q_(T), the pressure drop across valve 17a can be calculated basedon empirical data for the particular valve that is being employed. Forexample, when the flow rate is 200 milliliters per second, a series Hsingle shutoff valve having a one-half inch diameter from Snap-Tight,Inc. produces a pressure drop of 0.65 psi. This is stated by equation 7.

After the fluid passes through the valve 17a, it flows in a downwarddirection to manifold 17c. Due to this drop in height, a pressureincrease will occur. However, if the drop in height is suitably limited,then this pressure increase will not exceed the pressure drop in valve17a. For example, if the drop in height is six inches, then thispressure increase will only be approximately 0.2 psi as stated byequation 8.

Each time the fluid passes through one of the cooling modules 17d,additional pressure drops occur. Part of this pressure drop is caused bythe rapid expansion which the fluid undergoes when it enters the coolingmodule. This pressure drop can be expressed as an expansion head lossH_(E) as is stated by equation 9. In that equation, the term k_(e) is aconstant which depends upon the ratio of the diameters of components 17dand 17e. For the diameters as stated by equation 10, k_(e) is equal to0.42. Substituting that value of k_(e) into equation 9 yields equation11 which says the head loss H_(E) for the rapid expansion portion ofcomponent 17d is 4.05 inches.

Another pressure drop is also incurred each time the fluid leaves acooling module 17d due to the rapid contraction which occurs. Thispressure drop can be expressed as a contraction head loss H_(C) as isstated by equation 12. In that equation, k_(c) is a constant which alsodepends upon the diameter of the components 17d and 17e. For thediameter values given by equation 13, k_(c) equals 0.32. Substituting ak_(c) of 0.32 into equation 12 yields equation 14 which says thecontraction head loss H_(C) is 3.07 inches.

Thus the total head loss for one cooling module 17d is 4.05 inches plus3.07 inches or 7.14 inches. This is stated by equation 15. So long assuccessive cooling modules 17d are placed less than 7.14 inches apart,the pressure losses through those modules will be greater than thepressure increase which is caused by the fluid's drop in height as itpasses from the top of the printed circuit board to the bottom.

Next, reference should be made to FIG. 5 which is a set of equationsthat describe the operation of the FIG. 1 system under the conditionwhere pump 19 is turned off and valve 16 is open. This condition occurswhen fluid in the top reservoir 14 flows to the bottom reservoir 15under the force of gravity to purge air from the bottom reservoir.

Under this operating condition, it is again desirable to have the fluidpressure in the cooling modules 17b to be subatmospheric so that thefluid does not squirt out of the conduit 17. Thus, the previouslydescribed constraint of equation 4 in FIG. 4 must again be met; and itis rewritten as equation 1 in FIG. 5. Equation 1 contains a loss termL_(ab) which can be expressed as equation 2 wherein K_(c) is a constantfor valve 17a; V_(c) is the velocity of the fluid as it enters valve17a; n is the number of cooling modules 17d to point "b"; K_(b) is aconstant for one cooling module 17d; and V_(b) is the fluid velocity asit enters through cooling module 17d.

Based on the number of output ports from manifold 17c and the relativediameters of components 17b and 17c, the fluid velocities V_(b) andV_(c) are related as stated by equation 3. Substituting equations 2 and3 into equation 1 yields equation 4. There the velocity V_(c) is anunknown since pump 19 is off. However, the velocity V_(c) can beeliminated from equation 4 by applying Bernoulli's equation betweenpoints "a" and "e" in the FIG. 1 system, solving it for V_(c), andsubstituting the result into equation 4.

Equation 5 is Bernoulli's equation between points "a" and "e". In it,pressures P_(a) and P_(e) are both atmospheric since valve 16 is open;and velocity V_(a) is again zero. This is stated by equation 6.Substituting equation 6 into equation 5 yields equation 7.

Included in equation 7 is a loss term L_(ae). It equals all of thelosses which the fluid undergoes as it travels from point "a" to point"e". Those losses can be expressed as equation 8 wherein N is the totalnumber of cooling modules 17d in one column on printed circuit board 11;K_(d) is a constant for valve 17h; and V_(d) is the fluid velocity as itenters valve 17h.

Based on the number of input ports to manifold 17f and on the relativediameters of components 17d, 17e and 17g, the velocities at points "c","d" and "e" are related as stated by equation 9. Substituting equations8 and 9 into equation 7 yields equation 10. That equation can be solvedfor velocity V_(c) ; the result can then be substituted into equation 4;and this yields equation 11.

Equation 11 states a constraint on the system parameters which, if met,will cause the fluid pressure in the modules 17d to be subatmosphericwhen pump 19 is not running. One way in which equation 11 can be met, asan example, is as follows.

Let ρ=998 kg/m³ (water), K_(c) =1798 kg/m³, K_(d) =K_(c), K_(b) =396kg/m³, C_(b) =1.929, C_(e) =1, C_(d) =1, h_(a) =0, h_(e) =-30", h_(a)-h_(b) =6"+2n", N=9, and n is an integer from 1 to 9. Substituting thesevalues into equation 11 yields Table 1 below wherein X_(L) is the valueof the lefthand side of equation 11 in FIG. 5 and X_(R) is the value ofthe righthand side of equation 11.

                  TABLE 1                                                         ______________________________________                                        n        X.sub.L                                                                              X.sub.R    X.sub.L - X.sub.R                                                                    X.sub.L /X.sub.R                            ______________________________________                                        1        2,686  2,230      456    1.204                                       2        3,269  2,788      481    1.173                                       3        3,851  3,345      506    1.151                                       4        4,434  3,903      531    1.136                                       5        5,016  4,460      556    1.125                                       6        5,599  5,018      581    1.116                                       7        6,181  5,575      606    1.109                                       8        6,764  6,133      631    1.103                                       9        7,346  6,690      656    1.098                                       ______________________________________                                    

Turning now to FIGS. 6 and 7, the details of one preferred embodimentfor cooling module 17d will be described. This module includes a cover40, a spring 41, and a retainer 42. Components 40, 41, and 42 areintercoupled as shown and are attached to a ceramic integrated circuitpackage 43 which encapsulates one or more integrated circuit chips.Details of package 43 are shown, for example, in U.S. Pat. Nos.4,576,322 and 4,611,238.

Cover 40 includes a concave-shaped member 40a, an input port 40b, and anoutput port 40c. Member 40a has a rim 40d with a notch that is fittedwith an elastic seal ring 40e. That seal ring is compressed against aflat surface 43a of the integrated circuit package. Thus a passage isformed between surface 43a and the concave-shaped member 40a throughwhich fluid can flow to cool the integrated circuit package.

Spring 41 is an arc-shaped leaf spring. Also spring 41 is wide at itscenter and narrow at its ends. This is desirable because, as will beshown in detail in conjunction with FIG. 8, it allows the spring tomaintain a certain minimal force on the cover 40 and simultaneously notoverstress the spring even though various dimensions of the coolingmodule fluctuate from one module to another.

Retainer 42 includes a concave-shaped member 42a and a pair of headedpins 42b and 42c. Member 42a lies over the cover member 40a, and thepair of headed pins 42b and 42c are rigidly attached such as by brazingto a metal pad on the flat surface 43a of the integrated circuitpackage. Also, retainer member 42a has a pair of flanges 42d and 42ewith respective tapered openings 42f and 42g which are aligned with theheaded pins 42b and 42c.

When the headed pins are in alignment with the wide portion of thetapered openings, retainer member 42a can be pushed downward on spring41 such that the headed pins 42b and 42c pass through the openings 42eand 42f. This distorts and compresses spring 41. Then, member 42 can berotated clockwise by a few degrees such that the heads of the pins 42band 42c overlie the narrow portion of the tapered openings 42c and 42d.In that position, the heads of the pins cannot pass through theopenings. Thus the retainer member 42 is locked in place such thatspring 41 compresses the seal ring 40d with a predetermined stress.

Consider now FIG. 8 which is a set of equations that describe theoperation of spring 41. Equation 1 is obtained by summing the forceswhich act on the cover 40. In equation 1, F_(SP) is the force which thespring exerts on the cover 40; P is the gauge pressure of the fluid asit flows through the cover 40 (the difference between the absolute fluidpressure and atmospheric pressure); A is the surface area of the cover40 on which the pressure P acts in a vertical direction; and F_(SR) isthe force with which the seal ring 40e is compressed against surface43a.

Pressure P is determined by the analysis which was previously describedin conjunction with FIG. 4. Area A is determined by the size of theconcave-shaped member 40a. And a minimum value for force F_(SR) isselected such that the seal ring 40e will not leak.

Force F_(SP) can also be expressed in terms of a spring constant k timesthe deflection D of the ends of the spring 41. This is stated byequation 2. Substituting equation 2 into equation 1 yields equation 3.

In equation 3, the deflection D varies between a minimum value D_(min)and a maximum value D_(max). Those values depend upon variousmanufacturing tolerances for the components 40a, 42a, 42b and 42c. Forexample, the deflection D is smaller than nominal if components 42a, 42band 42c are taller than nominal and component 40a is shorter thannominal.

When the minimal deflection D_(min) occurs, the force which spring 41exerts must still be greater than the fluid force PA plus the minimumforce F_(SRmin) that needs to be maintained on the seal ring 40e inorder to prevent leaks. This, as stated by equation 4, is one constraintwhich must be met by spring 41.

In equation 4, the spring constant term k can be expressed in terms ofthe physical parameters of the spring 41. This is done via equation 5.There, L is the length of the spring; w_(s) is the width of the ends ofthe spring; w_(b) is the width of the center of the spring; h is thethickness of the spring, and E is the modulus of elasticity of thematerial from which the spring is made.

Another constraint which must be met by spring 41 concerns the maximumstress S that occurs in the spring. This stress S occurs at the centerof the spring. Equation 6 gives an expression for the stress S in termsof the force F_(SP) which the spring exerts and its physical parametersL, w_(s), and h. Again, the force F_(SP) which the spring exerts isequal to the spring constant k times the distance D by which the ends ofthe spring are deflected. This was stated above in equation 2.Substituting equation 2 into equation 6 yields equation 7.

In equation 7, the deflection D will have a maximum value D_(max) whencomponents 42a, 42b and 42c are manufactured relatively short andcomponent 40a is relatively tall. When that occurs, the stress S muststill be less than a value S_(max) at which the spring will permanentlydeform. This, as stated by equation 8, is a second constraint which mustbe met by spring 41.

As has been explained above, the pressure P of the fluid under normaloperating conditions will be subatmospheric. Thus, under normaloperating conditions, the term PA in equation 1 is negative; and thismakes the constraints of equations 4 and 8 easier to meet than if theterm PA was positive. So, for the purpose of demonstrating how thespring 41 operates under "worst case" conditions, assume now that thepressure P is above atmospheric.

For example, suppose PA is 13.5 pounds; F_(SRmin) is 1.5 pounds; S_(max)is 180 KPSI; D_(max) is D nominal plus 0.015 inches; D_(min) is Dnominal minus 0.015 inches; and D nominal is 0.190 inches. Under suchconditions, the constraints of equations 44 and 48 can be met by makingw_(b) =1.5 inches, w_(s) =0.25 inches; h=0.015 inches; L=1.50 inches;and E=20.33x10exp6 which is E for BeCu. These values cause the minimumspring force to be 16 pounds (which is greater than 13+5+1.5), and theycause the maximum spring stress to be 120 KPSI (which is less than 180KPSI).

Next, referring to FIG. 9, still another preferred embodiment of thecooling module 17d will be described in detail. This module includes acover 50, a spring 51, and a retainer 52 which are intercoupled to eachother and attach to an integrated circuit package 53 as shown.

Cover 50 is similar in shape to the previously described cover 40. Itincludes a concave-shaped member 50a, an input port 50b, and an outputport (not shown,) but which is in alignment with the input port 50b andin front of the spring 51). Cover 50 also has a rim 50d with a notchthat is fitted with an elastic seal ring 50e. A passage through whichthe fluid flows is formed by the concave member 50a, the seal ring 50e,and the surface 53a of the integrated circuit package.

By comparison, the retainer 52 has a totally different shape than thepreviously described retainer 42. Instead of being concave-shaped, it isuniform in width in a direction perpendicular to the plane of FIG. 9.Thus retainer 52 consists of one uniform width member 52a which liesabove cover 50 and two hook-shaped legs 52b and 52c which extend frommember 52a and clamp onto the bottom of the integrated circuit package53. When the legs 52b and 52c are clamped to package 53, member 52adeflects spring 51 which in turn exerts a force of predeterminedmagnitude on cover 50 such that the seal ring 50e does not leak.

Various preferred embodiments of the invention have now been describedin detail. In addition, however, many changes can be made to thesedetails without departing from the nature and spirit of the invention.For example, in the opening 14a of reservoir 14 in FIG. 1, a compliantmembrane could be added to prevent contaminants from reaching the fluidand to prevent the fluid from evaporating.

Accordingly, the invention is not to be limited to the describeddetailed embodiments but is defined by the appended claims.

What is claimed is:
 1. A liquid cooled circuit module, comprising:anintegrated circuit package; a cover having a rim which lies against saidintegrated circuit package, said cover being shaped to form a passagefor said liquid between said integrated circuit package and said cover;a retaining means, which is fastened to said integrated circuit package,and which includes a member that extends above said cover; and a spring,which is held in compression between said cover and said retaining meansmember; said spring being adapted to press said rim against saidintegrated circuit package with at least a predetermined minimal forcethat prevents leaks and at the same time not exceed a stress limit insaid spring.
 2. A module according to claim 1 wherein said retainingmeans includes headed pins which are fixedly attached to said integratedcircuit package, and wherein said retaining means member has taperedopenings which align with said pins and in which said headed pinsremovably lock.
 3. A module according to claim 1 wherein said retainingmeans member has hook-shaped legs which clamp onto said integratedcircuit package.
 4. A module according to claim 1 wherein said spring isadapted to maintain at least said minimal force on said rim andsimultaneously not exceed said stress limit, under the condition wherethe amount by which said spring is compressed varies due tomanufacturing tolerances within said cover and said retaining means. 5.A module according to claim 1 wherein said spring is a leaf springhaving a wide center and narrow ends.
 6. A module according to claim 1wherein said rim is fitted with an elastic seal ring.
 7. A module forcooling an electrical component with a liquid, comprising:a cover havinga rim which is shaped to lie against said electrical component and insuch position form a passage for said liquid between said electricalcomponent and said cover; a retaining means, which fastens to saidelectrical component, and which includes a member that extends abovesaid cover; and a compliant means, which is held in a distorted fashionbetween said cover and said retaining means member to press said rimagainst said electrical component with at least a predetermined minimalforce that prevents leaks.
 8. A module according to claim 7 wherein saidretaining means includes headed pins which fixedly attach to saidelectrical component, and wherein said retaining means member hastapered openings which align with said pins and in which said headedpins removably lock.
 9. A module according to claim 7 wherein saidretaining means member has hook-shaped legs which clamp onto saidelectrical component.
 10. A module for cooling an electrical componentwith a liquid, comprising:a cover having a rim which is shaped to lieagainst said electrical component and in such position form a passagefor said liquid between said electrical component and said cover; aretaining means, which fastens directly to said electrical component;and a compliant means, which is connected between said cover and saidretaining means and is adapted to change in shape to hold said rimagainst said electrical component with at least a predetermined minimalforce that prevents leaks.